1. Technical Field
This invention relates to the preparation of ethylene/1-olefin copolymers in the presence of selected nickel-containing catalysts.
2. Background
Various nickel-containing compounds, usually in complexed form, are known in the art as catalysts for polymerizing ethylene to linear 1-olefin oligomers. Certain of these catalysts, under selected conditions, are reported to polymerize ethylene to high molecular weight polyethylene. The copolymerization of ethylene with polar or non-polar 1-olefins, catalyzed by nickel-containing compounds, is unknown in the art.
Also well known in the art are copolymers of ethylene and non-polar or polar 1-olefin comonomers, prepared with nickel-free catalysts, such as the organometallic Ziegler-Natta coordination-type catalysts and free-radical catalysts. The most commonly used polar 1-olefins are of the formula CH.sub.2 .dbd.C(R)X wherein R is H or CH.sub.3 and X is a polar group, such as OC(O)CH.sub.3, OR' or CO.sub.2 R' wherein R' is alkyl, cylcoalkyl, aryl or halogen. Copolymers of ethylene and 1-olefinic comonomers containing polar functions attached other than to the vinyl group are also known, such comonomers being of the formula CH.sub.2 .dbd.CH(CH.sub.2).sub.n X wherein X is a polar group and n is an integer and is at least one, or of the formula CH.sub.2 .dbd.CHX(Z).sub.n wherein X is a hydrocarbon group having at least one carbon atom, Z is a polar group and n is at least one.
The difficulty of copolymerizing polar 1-olefin comonomers with ethylene using coordination-type catalysts, as compared to non-polar 1-olefins, is known to be greatest when the polar group is close to the vinyl group; it is also known to become easier the more closely the polar comonomer resembles a non-polar comonomer. Rules for achieving this similarity by various types of shielding are known in the art.
It has been discovered that certain, selected nickel-based catalysts which are known for use in the preparation of ethylene oligomers and, in some cases, polyethylene, are useful for preparing ethylene/1-olefin copolymers, including those containing polar substituents. Also discovered and disclosed herein are novel nickel-containing catalysts which are similarly useful.